1. Field of the Invention
The present invention relates to a lens system including lens elements of small diameters for projecting on to a screen in an enlarged fashion images from light valves such as mainly DMDs (Digital Micromirror Devices) for forming images by changing reflecting directions of light.
2. Description of the Related Art
Projectors utilizing DMDs as light valves are considered as being more advantageous in miniaturization than those utilizing other image forming methods. Currently, compact portable projectors have been well accepted by many users, and especially so are data projectors which are convenient for presentations.
In projectors which are developed for use as portable ones, reducing the thickness dimension is of importance, and it can be said that the reduction in thickness is one of the most important factors for projectors which are in many cases carried together with note-type personal computers or the like for combined use. As an example of a means for solving the problem, for example, the Japanese Unexamined Patent Publication No. 2003-121736 describes a design method for reducing the effective diameter of a projection lens.